Surface Termination of Fe3O4(111) Films Studied by CO Adsorption Revisited

Although the (111) surface of Fe3O4 (magnetite) has been investigated for more than 20 years, substantial controversy remains in the literature regarding the surface termination proposed based on structural and adsorption studies. The present article provides density functional theory results that allow to rationalize experimental results of infrared reflection-absorption spectroscopy and temperature-programmed desorption studies on CO adsorption, thus leading to a unified picture in which the Fe3O4(111) surface is terminated by a 1/4 monolayer of tetrahedrally coordinated Fe3+ ions on top of a close-packed oxygen layer as previously determined by low energy electron diffraction. However, surface defects play a crucial role in adsorption properties and may dominate chemical reactions on Fe3O4(111) when exposed to the ambient.